The present invention relates to a pipe processing system and more particularly to a method and apparatus for printing identification marks on steel pipes as they are manufactured and processed through a plant.
Pipes produced within steel plants generally must be provided with identifying marks or indicia which indicate particular production information including the production batch number or lot number, the date of manufacture, dimensional information relating to the pipe and destination information for the pipe. Such information has historically been placed on the pipes by means of stencils or, more recently, through use of ink jet printing heads driven by an appropriate microprocessor control circuit.
Further, the message to be printed on the pipe is typically typed into a terminal located near the printing area for the pipe and thus operators must be present at any printing terminals within the system in order to adjust the message to correspond to the particular type of pipe passing through the system.
Modern steel mills are capable of processing pipes at rates as high as 1,000 in./min. Thus, if it is necessary to enter a change in the indicia to be printed on the pipe, the system must either be slowed down or stopped while the operator types in a new message for the printer. In addition, the pipe processing system may also have to be shut down if one or more printing units malfunctions since proper tracking of the pipes through the steel plant is essential for inventory purposes. Such a plant shut down may result in financial losses of up to $5,000 per hour, and it is therefore essential to provide a processing system in which all of the components are as fail safe as possible.
U.S. Pat. No. 4,769,650 to Peng et al discloses a printing system for marking boxes which is similar to the systems currently in use for marking pipes in steel mills. The printing system includes a solenoid actuated nozzle module to spray ink in the form of a dot matrix onto the surface of an object and a speed sensor provides information to a microcomputer relating to the rate of the object in order to synchronize the sequence of ink spraying with the movement of the object.
While the above-described device of Peng et al is satisfactory for marking the planar surfaces of boxes, such a device suffers from certain drawbacks when put into use for printing on objects which have a radius of curvature, such as pipes. Specifically, the prior art print heads, such as shown by Peng et al, are typically formed by a plurality of spray nozzles aligned within a plane and which are positioned at a predetermined point along a conveyor path. Objects are conveyed past the spray head to receive appropriate markings in the form of dot matrix printing. When such print heads are used for printing on widely varying diameters of pipe, the print head may be satisfactory for printing on pipes having a large radius of curvature. However, when a pipe having a small radius of curvature passes through the system, the variation in distance between the various nozzles and the curved pipe surface may be large thereby resulting in the markings printing on the pipe being distorted.
Accordingly, there is a need for a printing system which is capable of printing on pipes having a wide range of diameters without distorting the message to be printed and which is capable of changing the print size and font quickly without causing undue delay in the processing of the pipe through the system. In addition, there is a need for a printing system which is economical and which may be easily replaced in the event of a malfunction occurring in the printing system, and the system should be easily controlled to alter the message to be printed to thereby minimize down time of the pipe processing system.
Further, there is a need for a pipe printing system which may be used as an integrated part of an inventory system within a steel mill for processing pipe such that messages to be printed on the pipes passing through the system may be altered automatically in accordance with messages from a main frame or host computer for controlling the inventory within the steel mill.